The present invention relates to a method and apparatus for converting sulfur dioxide in a gas, especially in a coal combustion exhaust gas, to sulfur.
Various methods for converting sulfur dioxide in a gas to sulfur have heretofore been proposed. For example, Japanese Patent Application Laid-Open Specification No. 120295/77 discloses a method in which sulfur dioxide in an exhaust gas is reduced to hydrogen sulfide and sulfur with a reducing gas such as hydrogen or carbon monoxide or hydrocarbon at the temperature between 950.degree. C. and 1250.degree. C., hydrogen sulfide formed at the reduction step is mixed with unreacted sulfur dioxide in the exhaust gas while controlling the amount of the reducing gas to be added to the reduction step so that the ratio of hydrogen sulfide to sulfur dioxide in the mixed gas is maintained at a predetermined level, preferably 2, and hydrogen sulfide formed at the reduction step is reacted with sulfur dioxide to convert hydrogen sulfide to sulfur according to Claus reaction formula.
The known method, however, has such disadvantage that the ratio of removal of sulfur is very low, since it is very difficult to maintain the ratio of hydrogen sulfide to sulfur dioxide in the gas after the reduction reaction only by controlling the amount of the reducing gas to be added. Namely, this ratio is greatly changed according to the composition of the exhaust gas fed to the reduction step and the reduction reaction conditions. If this ratio deviates from 2, either of SO.sub.2 and H.sub.2 S is left in the treated gas. The composition of the exhaust gas is changed according to combustion conditions, absorption conditions and desorption conditions.